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26th of November 2021
The Parkes variable baseline interferometer
by Ron Ekers
Yesterday's ADAP describes the variable baseline interferometer, used at the Parkes Observatory in the late 1960s and early 1970s, which combined the signals from the 18m (60-foot) "Kennedy" antenna (Giyalung Guluman) and the 64m (210-foot) Dish (Murriyang). This innovative system allowed the one-dimensional structure of radio sources to be determined in about 15 minutes, as opposed to the months required by fixed-spacing interferomemters elsewhere. The image above is a variable baseline visibility record of the double-lobed radio galaxy Pictor A showing the fringes and the classic double-source amplitude modulation. The x-axis is the baseline length in feet, with the amplitudes at two frequencies (467 and 1401MHz), measured simultaneously, plotted. (Ron gives more details of the variable baseline interferometer in a video available from the Parkes 60th webpage.)

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